American scientists fabricated a battery through a two-step enclosed space sublimation process, and applied a seed layer to a molybdenum-coated soda lime glass substrate through rapid thermal evaporation. They claim that this promotes the growth of a high-quality Sb2Se3 absorber layer with high crystallinity and large columnar grains.
Antimony selenide (Sb2Se3) is a p-type inorganic semiconductor with a one-dimensional crystal structure with a direct band gap ranging from 1.2 eV to 1.9 eV. It has excellent photoelectric properties. In recent years, it has also been used as an absorbent material for the manufacture of solar cells. The efficiency achieved by this type of equipment has reached 5% to 9.2%.
These efficiency levels are still far behind other thin film technologies, such as batteries based on copper, indium, gallium and selenium (CISG), cadmium telluride (CdTe), chalcopyrite (CZTSSe) and amorphous silicon (a-Si). This technological gap may depend on the fact that the scientific community of Sb2Se3 battery technology still knows little about the characteristics of mobility, carrier lifetime, diffusion length, defect depth, defect density, and tailing, because this type of battery technology Not many devices have been fabricated so far.
American scientists at the University of Toledo recently tried to study this cell structure. They developed a device with a power conversion efficiency of 8.5%.
"The efficiency is measured in our own laboratory, so it is internally certified," researcher Suman Rijal told Photovoltaic Magazine. "These batteries can be used to produce solar energy and can also be used as photocathodes for the production of hydrogen through solar water splitting."
The battery is constructed using two-step enclosed space sublimation (CSS), a physical vapor deposition method for producing thin films. It involves semiconductors that evaporate below 800 degrees Celsius, and these semiconductors are coated on a substrate under vacuum and atmospheric pressure.
"This is a sublimation deposition method that can be used in commercial production," Rijal said.
The scientists applied a seed layer to a soda lime glass substrate coated with molybdenum (Mo) through rapid thermal evaporation (RTE). They stated that this enables the templated growth of the vertically-oriented Sb2Se3 seed layer, which in turn enables the growth of a high-quality Sb2Se3 absorber layer with high crystallinity and large columnar grains, while also avoiding the formation of voids at the back interface. .
"The seed layer plays a vital role in controlling the crystalline quality and preferred orientation of the Sb2Se3 film and its interface characteristics," the scientists said, noting that the growth of Sb2Se3 bands can be mainly oriented in two groups of directions. Strips oriented vertically on the surface of the substrate are preferred.
The battery developed with this configuration initially achieved an efficiency of 7.47%, an open circuit voltage of 459 mV, a short circuit current of 26.54 mA cm 2 and a fill factor of 61.39%. After post-deposition annealing in air to passivate the bulk defects in the Sb2Se3 absorber, the device reached 8.5%.
"Air annealing effectively reduces the density of defects and reduces their activation energy," the scientists said. They also claim that their research shows that high-performance Sb2Se3 solar cells can be developed through a method they define as "easy and effective."
They shared the technical details of the cell in the "template growth and passivation of vertically-oriented antimony selenide thin films for high-efficiency solar cells in substrate configurations" recently published on Advanced Functional Materials.
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More articles by Emiliano Bellini
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